The invention is generally related to the field of semiconductor processing and more specifically to a metal fuse process.
In some integrated circuits, alternate interconnect paths are created to increase yield. For example, in SRAM circuits, after the last interconnect level is formed, the functionality of the device is measured. Defective interconnect paths are severed and replaced, with alternative interconnect paths. The defective interconnect paths are severed by xe2x80x9cblowingxe2x80x9d a fuse. During this process, a high power laser is directed at fuses that need to be removed. As a result, the fuse is for the most part, vaporized by the high power laser pulse. A wet etch is then used to remove any remaining fuse material from the blown fuse link as well as material from the fuse that may have been redeposited on the surface during the blowing process.
One prior art fuse process is shown in FIGS. 1A-1D. The top metal interconnect layer is used to form both fuses, like fuse 30 and probe pads, like probe pad 40. The top metal interconnect comprises aluminum 42 with an overlying TiN barrier layer 44. 8000 xc3x85 of oxide 52 are deposited using a high-density plasma (HDP) process. A resist pattern 54 is formed exposing the areas of oxide 52 over both the fuses and the probe pads, as shown in FIG. 1A. A single etch is then used to expose the fuses 30 and probe pads 40, as shown in FIG. 1B. An etch chemistry is used that etches both oxide and TiN. As a result of the etch and overetch required to ensure that all desired areas across the wafer are cleared, the fuse links 30 are degraded.
The circuits are then probed to determine which fuse links should be blown to fix defective circuits.
Next, a 3000 xc3x85 conformal oxide layer 56 is deposited over the structure, as shown in FIG. 1C. Layer 56 completely covers the exposed fuses 30 and provides protection for the exposed aluminum of the probe pads 40. A laser pulse is then directed towards the fuses that need to be removed. The fuse 30 cracks or breaks off at the weakest point, as shown in FIG. 1D. A wet etch is then used to wash away any remaining broken fuses and debris and dissolve fuse links that may be still attached through cracks in the conformal oxide.
Unfortunately, a blown fuse that does not crack correctly can jeopardize adjacent fuses that may still be desired. As a result, this process may result in degraded or even missing fuses.
The invention is a metal fuse process that uses a thinner (e.g., 6000 xc3x85) oxide over the top interconnect. Because the oxide is thin at the upper corners of the fuse, the oxide cracks over the fuse during a laser pulse. A wet etch is then used to dissolve the exposed fuses.
An advantage of the invention is providing a metal fuse process the offers improved yield by avoiding over etching of fuses.
This and other advantages will be apparent to those of ordinary skill in the art having reference to the specification in conjunction with the drawings.